512 Geological Society. 



GEOLOGICAL SOCIETY. 



Nov. 18, 1840. — Mr. Lyell's memoir " On the Geological Evi- 

 dence of the former existence of Glaciers in Forfarshire," was read. 



Three classes of pha^nomena connected with the transported 

 superficial detritus of Forfarshire, Mr. Lyell had referred, for several 

 years, to the action of drifting ice; namely, 1st, the occurrence of 

 erratics or vast boulders on the tops and sides of hills at various 

 heights, as well as in the bottoms of the valleys, and far from the 

 parent rocks ; 2ndly, the want of stratification in the larger portion 

 of the boulder formation or till ; and 3rdly, the curvatures and con- 

 tortions of many of the incoherent strata of gravel or of clay resting 

 upon the unstratified till*. When, however, he attempted to apply 

 the theory of drifting ice over a submerged country to facts with 

 which he had been long acquainted in Forfarshire, he found great 

 difficulty in accounting for the constant subtei-jDosition of the till 

 with boulders to the stratified deposits of loam and gravel ; for the 

 till ascending to higher levels than the gravel, and often forming 

 mounds which nearly block up the dramage of certain glens and 

 straths ; for its constituting, with a capping of stratified matter, 

 narrow ridges, which frequently surround lake-swamps and peat- 

 mosses ; and for the total absence of organic remains in the till. 



Since, however. Professor Agassiz's extension to Scotland of the 

 glacial theory, and its attendant phsenomena, Mr. Lyell has re-ex- 

 amined a considerable portion of Forfarshire, and having become 

 convinced that glaciers existed for a long time in the Grampians, 

 and extended into the low country, many of his previous difliculties 

 have been removed. There are, nevertheless, facts connected with 

 the ridges of stratified materials resting upon till, which he is unable 

 to exjilain. He also states, that though he had for years inferred 

 from the evidence of fossil shells sent to him from Canada by Capt. 

 Bayfield, that the climate of North America, in the latitude of Que- 

 bec, was far more intensely cold at one period than it is nowf, yet, 

 that his thoughts had been diverted from the consideration of a long- 

 continued covering of snow on the Scottish mountains, by the know- 

 ledge that the climate of Great Britain, during the several tertiary 

 epochs, was warmer than it is at present. He is of opinion that, 

 during a period immediately antecedent to the existing, several os- 

 cillations of temperature may have occurred in the northern hemi- 

 sphere. 



Forfarshire, Mr. Lyell divides geologically into three principal 

 districts: 1st, the Grampians, composed of granite, gneiss, mica- 

 slate, and clay-slate, flanked by a lower range of vertical beds of 

 old red sandstone, associated with trap ; 2ndly, the great syncli- 

 nal trough of Strathmore, occupied by the middle and newer mem- 



* See Mr. Lyell's paper on the Norfolk Drift, Phil. Mag., May 1840, 

 and the Abstract of the paper in the Proceedings of the Society, vol. iii. p. 

 171. 



t See Proceedings, vol. iii. p. 119 [or L. & E. Phil. Mag. vol. xv. p. 399]. 



